Perpetual calendars are calendars which can be used year after year by simply setting the calendar in the appropriate position for the current year. Thus, perpetual calendars are convenient devices to own and use. A number of mechanical perpetual calendar systems are known in the art, ranging from complex mechanical machinery to simpler card-based systems.
U.S. Pat. No. 217,433 issued Jul. 8, 1979 to E. J. Trum discloses a perpetual calendar comprising a fixed base card onto which is marked days of the month in rows, ie. in calendar form. Two strips of removable cards lie above and below the base card and have printed on them the month, year and days of the week. One strip indicates the month last past and the other strip the current month. The days of the week marked on the strips are aligned with the rows of the days of the month marked on the base card. As the months expire, the topmost card of each strip is removed to show the next cycle of the current and past month and the days of the week appropriately aligned with the days of the month on the base card. Eventually, of course, the strips need to be replenished.
U.S. Pat. No. 239,867 issued Apr. 5, 1881 to J. G. Smith describes a calendar ink stand having a nose around which is arranged a band having on its outer surface the days of the week arranged in order and can be turned, as required. The top of the ink stand is divided into five concentric rings and seven sectors in order to display the days of the month from 1 to 31. On the bottom of the ink stand there is a rim and located concentrically therein is a band having the names of the month displayed on the outer surface thereof. The proper month can be exposed at one point by means of a window in the rim. It is necessary for the user to always know how many days the current month has in order to be alerted thereon to change the day of the week setting to the first of the next month.
U.S. Pat. No. 256,396 issued Apr. 11, 1882 to J. G. Smith discloses a calendar ink flask wherein the days of the month are fixedly displayed on the side of the flask and the current month is displayed through a window in the base of the flask. On the neck of the flask lies an adjustable neck band having the days of the week arranged in order thereon. The neck band can be turned so as to bring the proper day of the week to correspond to the first of the month. It is necessary for the user to always know how many days the current month has in order to change the day of the week setting to the first of the next month at the appropriate time.
U.K. patent No. 1,250,871 published Oct. 20, 1971 to J. J. Robinson discloses a complex mechanical perpetual calendar system. The mechanical calendar comprises a casing formed with four viewing apertures and four annular gear units with data thereon rotatably mounted correspondingly to the casing so as to exhibit the data through the apertures. The first gear unit shows the year, the second the months of the year, the third the days of the week, and the fourth the date, i.e. numerical day of the month. Actuating means allow the first and third gear units to be selectively rotated independently of the second and fourth gear units to simultaneously alter the year numeral and day displayed. The second and fourth gear units can be rotated independently of the first and third gear units to simultaneously alter the month and date displayed. In order that the correct number of days be shown for the month, the calendar employs on the date gear unit four date covers, each comprising an arcuate strip provided with a rearward projection that extends through a horizontal throughslit formed in each date quadrant. This calendar, by virtue of its relatively complex mechanics, is a relatively expensive item to produce.